Telemeter system



o. EPPEIISTEIII.4

TELEMETER SYSTEM.

APPLICATION FILED APR. I1. 19M.

1,414,779. 1 l Patented May 2 1922.

4 SHEETS-SHEET 2.

0. EPPENSTEIN.

TELEMETER SYSTEM.

APPLICATION FILED APR. I7, 19m.

1,414,279., Patented May 2, 1922..

rf j' 4 SHEETS-SHEET 3. 5 54 gq/5a @35250 L| IiilliiiiIilII I IIIIIII 0. EPPENSTEIN.

TELEMETER SYSTEM.

APPLICATION FILED APR. 1?..I9I4.

1,414,779., Patenten/[ay 2, 1,922.

l I 4 SHEETS-SHEET 4.

UNITED STATES PATENT OFFICE.

OTTO EPPENSTEIN, OF JENA, GERMANY, ASSIGNOR T THE FIRM OF` CARL ZEISS, 0F

JENA., GERMANY. I

TELEMETER SYSTEM.

Specication of Letters Patent.

Patented May 2, 1922.

Application led April 17, 1914. Serial No. 832,628.

(GRANTED UNDER THE PROVISIONS 0F TYIIE ACT 0F MARCHA 3, 1921, 41 STAT. L., 1313.)

To all whom it may concern;

Be it known that I, OTTO EPPENSTEIN, a citizen of the German Empire, residing at Jena, Germany, have invented a new and useful Telemeter System, of -which the following is a specification.

The invention relates to a system of te-` lemeters, each of which comprises, for measuring purposes, a setting device and each of which 1s intended for an observer. Acc'ording to the invention the said setting device is Icaused t0 act on a joint-indicating device, so that on the scale of the latter there is indicated automatically a mean value of the values given by the single telemeters. It is probable, that in the said mean value, which has already sometimes been Jformed by calculation, the incidental errors of the single values and, a considerable number of telemeters coacting, the personal errors of the single observers as well (as the latter device.

" same.

errors mayv also be positive or negative) have compensated one another. hIn addition to this, the said mean value corresponds, the telemeters being placed at different stations, if only their distance from one another relatively to the distance of the object to be measured be comparatively small, to the distance of a mean station from the object to be measured.

The effect of the setting device on the joint indicatin device need not oalways be the hen it is a matter of uniting the readings of telemeters having a compara tively small distance apart to one mean value their setting devices will with advantage be mechanically interconnected for the purpose of acting on the joint indicating When there are only two telemeters and these two telemeters are adjacent to one another, it is of especial advantage to let a common carrier serve for their reception, which carrier may be formed as a common .casing for the two telemeters". Thesaid carrier makes it possible on the one hand, to make the mechanical connection of the setting devices into a permanent one, so that a, repeated adjustment of the joint indicating other one. the setting devices of the two telemeters each comprise a system of refracting. prisms, they may be connected together by means of differential gearing, that member of the `gearmg, which is moved by the two setting devices (the planet pinion serving for actuatlngthe joint indicating device. Accord- When in such an arrangement ing as the said indicating device is tol peradopt differential gearing, the two setting devices may, for example, be connected together in such a manner that one of them moves the scale and the` other the index of the joint indicating device.

In order to unite -the readings of adjacent telemeters, for the reception of which a common carrier is again employed, to a mean value, it is also possible to connect anoptical system with this carrier, by means of which an image of one of the two members of' the joint indicating device of the telemeters' (viz. the index-mark or the scale) is formed on-the other one or on an image of' the same7 the setting devices of the telemeters influencing the position of the image of the one member relatively to the other u',

a mean value is to be formed, the setting de-i vice of 'each telemeterI may be with advantage coupled tothe shiftable part of the transmitter of an alternating current long d istanceain'dicator and all these-.transmitters 'allowed to act on a single receiver, whichv is' connected Ito an indicating device, the shift.- able part of the receiver. being put in parallel with the shiftable parts of the transmittersjand its non-shiittable part andl the non-shiftable part of each transmitter being connected up with an alternating current network in such a manner that in the nonshiftable parts av rotating field is created.

Whenthe system consists of two adjacent uniocu-lar coincidence telemeters, the baselinesof which are of about the same length and the setting devices of which act on a joint indicating device, and if 'these telemeters can` be connected up relatively to each other in such a manner that their basei lines become parallel. to one another and that each of the two ray pencil systems' emerging from. the first telemeter is presented to the corresponding entrance openingv of the second telemeter (in telemeters, the baselines of which have ditlerent lengths, or in telemeters,the entrance openings of which are turned away lfrom each other, for in .stance by means of suitable reflecting systems), so that the image of an object, whlch lies or an image of which is formed in t-he focal plane of the objectives of the first telemeter, is formed in the focal planeof the objectives of the second telemeter,the approxima-te arithmetical mean value of the v distances of the object to be measured can be given on the joint indicating device by the two telemeters, even without either of the twotele-meters being correctly adjusted. For, if the ray pencilsystem emerging'from the first telemeter, as may be seenfrom German patent specification 251,041 for a special case, be each presented to the corre- `sponding entrance opening of the second telemeter in such a manner that the angle formed by each emerging ray pencil system with the base-line of t-he particular telemeter is equal tothe supplement of the angle A formed4 by the ray pencil system belonging to 1t entering the other telemeter-with the Abase-line of the latter tele-meter (which is of itself thecase in telemeters, the base-lines of which are of ejqual'- len h and the entrance openings of which ace each other),

andwhen the state of adjustment of the first telemeter deviates from the correct adjustment and when the setting. device of this` telemeter is set in such a manner that the. vcorresponding indicating device indicates the value infinitely, and thereuponl the lSetting of the indicating device of the second telemeter, coincidence having been obtained for the said object (which hes or of which an image is formed in the focalI plane Yof the objectives of the first telemeter is altered in such'a manner that the said indica-ting' device likewise indicates the value infinity, the two-parallax angles belonging to that object, for which the value infinitely 'is given on the two-indicating devices, diierv trom \zero and are equally great, theyI have, h'owever, opposite s1 s. When the joint indicating device is iiiewise set to the value ininity, its scale having to be divided in such a manner that, on setting the indicating devices of the two telemeters to the same inf dication, the samevalue-is given also on-it, and when the movements of the said two in- Laramie Vdicating devices are transmitted yto the joint 'the other one, whereas` the indication of the joint indicating device corresponds approximately to the said true value. This may be proved-by a similar train of thought also for binocular telemeters with setting means,

such as are known through the German pat-- ent specification 255,955.`

When t-he objective prisms of the telemeters are located in front of the objectives,

the objective prisms of one of the telemeters will be, in order )that the above described settings of the two instruments may be et'- fected, dispod with advantage in such a manner that they can be changed from their position, which corresponds to the measuring condition of t-he telemeter, into a position, in which they face the objectiveprisms of the. second telemeter. When the baselines of the two telemeters are parallel to one another, a joint carrier ma (in the case of adjacent telemeters) be wit advantage ernployed for their reception, whlch carrier may be formed as a joint casing, and, in

the case of o-ne of the telemeters, on the one Vhand the objective prisms are disposed in such a manner that, on being rotated 1n the.

plane of triangulation by 90, they can-be l turned to face the entrance surfaces of the objective prisms of the othertelemeter with what were so far their emergence surface, and on the other hand the objectives and the separating prism System are disposed 1n such a manner that they can be jointly rotated through 180 about an axis, which is parallel to the baselines, the 'said axis of rotation having such a position that' the objective prismseach again come to lie in the g path of rays of the corresponding objective.

11E, however, the setting device does not take4 part in the said rotation through 10, 'care A. must be taken, that'any errors of adjustment .arising thereby are compensated.

.lin "the annexed drawing: Fig. 1 is a dla'- grammaticK representation of the telemeter system according to the inventlon. Figs. 2 to 4 show a .constructional example offthe new telemeter system, Fig. 2 being a vertical section through 'the joint easing, Fig. 3 a

, plan view land lEig. 4 a cross-section on line '1i- 4c OFig. 2. `lFig's. 5 to 8 show a; second :construct-ional example of the new teliemeter system, Fig. 5 being a vertical section throughthe joint casing, Fig. 6 a. Vvertical section on line 6-6 of Fig. 7, Fig. l7 a plan view partly in section and Fig. 8 a crosssection onA line 8-8 of Fig. 7. Figs. 9 to 11 show a third constructional example of the new telemeter system, comprising 3 telemeters, Fig. 9 being .a plan view of'one of the three telemeters, Fig. 10 a diagrammatic representation of the whole telemeter system to a larger scale, only that part of each telemeter being shown, which contains the setting device, and Fig. 11 a side elevation of the said part. Figs. 12 to 14 show a fourth constructional example of the new telemeter system, Fig. 12 being an elevation partly in section, Fig. 13 a horizontal section through the joint casing on line 13-13 of Fig.`12, containing the common sighting plane of the telemeters, and Fig. 14 a cross-sectionson line 14-14 of Fig. 13, containing the .axes of inspection. y

In Fig. 1 the system. consists of two uniocular telemeters of equal dimensions, having a common" base-line outside the vinstrument. Each of the twotelemeterscomprises an objective 1, a twice reflecting prism 2, whichv deflects the entering rays by 90, an isoscelesFright-angled ridgeLprism 3, a Ramsden ocular 4 and a Rochon prism 5, which is displaceable vin the directionof the optical axis, the telemeteis` having such a relative position, that the direction of entrance of the rays is thesame `for both of them, while corresponding displacementsl of the Rochon prisms .are parallelly andoppositely directed. One of the Rochon prisms is connected with the scale 6 and the other with the index 7 of an indicating device, which is common to the two telemeters. The scale 6 is parallel to the direction of displacement oi? the prisms and is divided in such a manner that-the index 7 gives on it the arithmetical mean value of the displacements of the Rochon prisms, which value corresponds approxmately to the arithmetical mean value of the distances measured by the separate telemeters.

In the constructional example', Figs. 2 to 4, the system consists of two uniocular coincidence telemeters, which are disposed one above the other in a joint casing and the base-lines of which are parallel to one` an-v other and of equal length and each belong to the instrument, one image in the case of' each telemeter being inverted in the direction perpendicular to the base-line. The setting devices of the two. telemeters comprise. each a displaceable refracting prism and are connected together by difierential. gearing, thie crown wheels of which are represented by racks. the two telemeters are disposed in the joint casing 8 and comprise each two objectives 9, two twice reflecting prisms 10, which are The optical systems of located in frontv of the. said objectives, a' separa-ting rism system 11 and an astronomical ocu ar 12. While the entrance surfaces of the.l prisms 10 ,of both telemeters face one and the sameside of the casing, the oculars 12 are located at different sides, so that their directions 'of inspection are opposite to one another. The optical part of each of the two measuring devices is formed by a' refracting prism 13, which is displaceable in the horizontal direction and is dislv posed between the separating prism system and the objective lyingl in the.drawing to the rightof each telemeter. Each; of these prisms 13 is connected with a scale 14, which can be observed at the inspection side of'` the telemeter belonging to it through a .window 15 in the casing, which bears the corresponding index 16. The two prisms 13 are so chosen and disposed that, in order to pass from the. setting of the two measuring de-I vices for a first common object to the setting for a second common object, the two prisms must be displaced by equal amounts and in the same directions. For being set eac-h, 90 prism carrier 17 is fitted with a. .rack 18, with which a pinion 19 engages, which can be actuated by means of a milled head 20. Two further racks 21, whichr each belong to one of the prism carriers 17 and areparallel to the direction of displacement of the Aprisms '13, engage with their teeth facing each other with a toothed wheel 22. This' .toothed wheel is rotatably mounted on. an .arbor 23; which is guided by means of two' slides 24 in the casing 8 in the direction of displacement of the prisms 13. Each of the slides is fitted with a/scale 25, which has the same divisions as the scales '14 of the setting devices, and can be observed through a winr dow 26 'in the casing 8, which bears the cor-- responding index 27. B. means of these indicatii'ig devices 25, 2g the l arithmetical 4mean value of the prism displacements is inof the distances measured by the separate telemeters. l

In the constructional example,Fi'gs. 5 to 115 8, the system again consists of two uniocular coincidence telemeters disposed one above the other in a joint casing, thebaselines of which telemeters are parallel to one another andof equal length and each i' belong to the instriiment,`one of the images in each telemeter being inverted in the di. rection perpendicular to the base-line. Each telemeter comprises two objectives 28, two twice reflecting prisms 29, which are lo- 125 catedin front of these objectives, a'separat-y ing prism system 30 and an astronomical ocular 31, a joint `casing 32 serving'lfor the reception of the said two optical. s stems. While the lentrance surfaces of the prisms '29 130 Vin front of the same of each telemeter.

als

of both telemeters tace one and the same side,r of the casing, the oculars 31 lie at different sides, sol that their directions 'of inspectin are opposite to one another. 'llhe optical part of each of the' two measuring devices comprises two equal refracting prisms 33 and 34, which are rotatable in opposite directions, but through the same angle, and lie between the objective which lies to the right in the drawing, and the prism localtald e movement of these retracting prisms is effected from the arbor of the measuring drum 35 by means of bevel wheels 36, 37 and 38. The twomeasuring devices are chosen and disposed in such a manner that, inv order to pass romthe setting for 'a first common object to the setting for a second common object, two prisms, which correspond to one anrays, each time through 90.

other and each belong to one of the two meas` uring devices, for instance the two prisms33, each of which is adjacent to the objective prism belonging to it, are to be rotated by equal amounts, but in opposite directions. On that sideof lthe joint casing 32' of the two telemeters, which is remote fromthe ob- -ject to be measured, there is fixed an optical system, whichcomprises an objective 39, a collective lens 40, a lens of reversion-41 and a Ramsden ocular 42, three isosceles rightangled prisms 43 being introduced into the path of the rays for thrice deflecting lthe` The optical system serves for forming an image 'of an index 44 disposed in front of its objective 39 on a scale 45 lying in the focal plane of the ocular, which lscale together with the vindex represents the indicating device common to the two telemeters. 'lhe influence of the setting Vdevices on the said'indicatingI device is eH'ected in each case by means ofxa V direct vision (Amici) prism 46,-the mountjournalled between the objective 39 and the ing 47 of one of these prisms being rotatably collective lens l40 and that of the other prism betweenthe collective lens 40 and the lens of reversion 41 in such a manner that the axis of rotation of each prism is represented by the common axis of the entering and emerging ray pencil and coincides with the axis of the optical system. For transmit#v ting the setting movements the two refracting prisms 33, which belong each to one of the two setting devices and are adjacent eachA to the right-hand corresponding objective prism, are each fitted with toothing48, with which meshes a toothed lwheel 49 of one and oi the other prism mounting 47 respectively,

- which toothed wheels havethe same number of teeth as the said toothing. The rotation of such a direct vision yprism 46 will cause, asis well known, the image of the index 44 to rotate relatively to the scale 45 through an angle, which is twice as great as the angle of rotation of the prism' itself. 'llwo image/e such direct vision prisms, which, seen in the direction of the light, 'are rotated in the same sense, therefore act on .the -image of the index in such a manner that it is rotated through an angle, which is equal to twice the sum of the angles of rotation of the .said prisms. As it has been assumed, that the number. of teeth of thetoothings 48 and .49 is the same, so that the refracting prism 33 of one of the twosetting devices andthe corresponding direct "vision prism 46 can rotate only through equal angles, it follows,

that the -image ,of the index is subject to. a

rotation, which'is equal to an angle oftwie the sum of the angles of rotation of the said refracting prisms 33. Now, in order .that

.the arithmetical mean value of these angles of rotation will be indicated on the scale, which value approximately corresponds to 'the arithmetical mean valuel of the kvalues' 48 and 49 have equal numbers ofteeth, that only an angle of rotation of the refracting prisms of is permissable. l

ln the next constructional example, lf'igs. 9 to 11, the system consists of three uniocul ar coincidence telemeters having the base-line within the instrument, one of the images in each telemeter being inverted in the direction perpendicular to the base-line. The optical System ofea-ch of the three telemeters consist of two objectives 50, two twice reecting prisms 51 located infront of these objectives, a separating prism system 52 and an astronomical ocular 53. 'lhel optical part of each setting device is formed by a refracting prism 54, which is displace# -able vin the directionof the base-line, is disposed betwen the separating prism system and the right-hand objective of each telemeter and the movement of which is to be supposedas being eected4 from the arbor of a toothed wheel 55 by means of rack and pinion drive. lin order to be able to obtain thearithmetical mean value from the displacements of the refracting prisms, which mean value correspondsfor pro ortionately small relative distances of the t ree telemeters as compared with the distance of the object to be measured-approximately to 'the arithmetical mean value of the dis- 1 tances oit/the separate telemeters from the object tol be4 measured, each telemeter is fitted with the transmitter of analternating current long distance indicator,I which is actu* ated bytwo currentscoming from a generator 56, which are 90 out .of phase. The

lines of these currents are marked 57 and 58 'and the equalizing line 59. 'llhe stalbelonging to a scale 69.

. tionary part of each transmitter consistsof while the movably disposed part comprises.

only one pair of coils 63, the single coils of which also form a diameter ofthe said ring. The pair of coils -63 is xed to a toothed wheel 64, which meshes with the' toothed wheel 55 of the setting device of the corresponding telemeter and can be actuated by means of a milled head 65, the toothed wheel 64 having such a number of teeth that one revolution of this wheel corresponds to the total displacement of the refracting prism 54. The three transmitters of the long distance indicator are served by a single receiver, the stationary part of which consists of two crossed coils 66 and 67, while its movable part comprises a moving coil 68, which is fitted with an index 70 Now the transmitters and the receiver are connected up in lsuch a manner that, on the one hand, the

coils 61 and the coil -66 are connected to the circuits 57 and 59 and the coils 62 and the coil 67 to the circuits 58 and "59, so that in the stationary parts of the transmitters and inv that ofthe receiver a rotating field systeml 61, 62, act on the moving coil 68 of the receiver in sucha manner that .the index ofthe same phase is created, and that, on the other hand, the coils 63 and the coil 68 are connected in arallel by means :of the lines 71 and 72. he effect of this'is, that the currents induced, on setting the telemeters, in the pairs of coils 63, in consequence of a rotation of each of the pairs of movable coils 63 of the transmitters relatively to the corresponding stationary coil 70 indicates on the scale 69 the mean value of the said rotations, which'y value approximately corresponds to the mean-value of the distances of the singlej'telemetersfrom the l object tobe measured.

In the last constructional example of the invention, Figs. 12 to 14, the system consists of two uniocular coincidence telemeters, which are disposed one behind the other in a joint casing and the base-lines of which are parallel to one another, are of different lengthfand belong-each to the instrument,-

one of the images in each telemeter being inverted in the direction perpendicular to the base-line. .For 'acting upon\the joint vindicating device, the two setting devices are again connected together by means voit diderential gearing. In the joint casing 73 there' are disposed two inner tubes, one

of which, 74, is ixed to the casing, while the other, 75, is journalled, so-as to .be

' rotatable about its axis, and canbe'rotated,

through the turning-of a milled head 76 through 360, .by means of a pair of bevel wheels 77, 78 through 180. The extreme positions of the inner tube are indicated on lars 82 belonging each to one of the telemeters are each fixed opposite an opening 83 of the particular inner tube to the outside of the casing in such amanner that their axes of inspection' are directed oppositel'y to each other. The objective prisms 84, which belong to the rear telemeter (with the immovable inner `tube 74), are fixed in the casing, whereas the objective prisms 85 belonging to the front telemeter canbe rotated by means of a milled head 86 through 90 in the common sighting plane of the telemeters. In .one of their extreme positions these objective prisms 85 face, as do also those of the second telemeter, the object toI be measured and determine a baseline, which is greater than that of the said second telemeter, while in their other extreme position they vface with what were so far their emergence surfaces 87 the entrance surfaces 88 ofthe objective prisms of the second telemeter. The said two extreme positions are indicated on the milled head 86 by means 'of an index 89`fitted to the casing.l The loptical part of each of the two measuringdevices again comprises two equal refracting prisms 90 and 91, which are rotatable in opposite directions, but

through equal angles and which lie between the right-hand o -jective and the prism located in front of it of each telemeter, and

the movement of these refracting prisms vis effected from the arbor of the setting drum 92, which forms with the `index 93 fitted on the` casing the indicating device of the particular telemeter, by means of bevel wheels 94, 95 and 96.' The two measuring devices are chosen and disposed in such a manner that, for passing from the settingfor a first 1 the objective prism belonging to it, are to be rotated by equal amounts, but in opposite directions.- These two prisms 90 are each connectedwith one of thel two crownwheels 97 of4 a differential gearing, oneof-v them directly and the other by means of a pair of gear wheelsv 98, each of which has the -ll same number of teeth. The planet pinion .99 of the said differential gearing'. is rotata# on an arbor '100,- which 1s bly journalled fixed tov a box 101, and this box bears on its outer periphery a scale 102,`which may be' bservedthrough a window 103 1n the casing and forms together with an index 104 on the said Window the indicatin device commento the two telemeters. T is scale isso divided that, on the indicating devices of the two telemeters ,being set to corre'- Isponding indications, the same value is inditelemeter, an optical system is provided,

consisting of an objective 105 and of two isosceles right-angled reflecting prisms 106 and 107. j

vThe 'telemeter system is adjusted in the following manner: The inner tube 7 5 of the front telemeter is brought by means of the milled head 76 into a position, in which its lopening 83 faces the reflecting prism 107,

and the two objective prisms 85 are each moved by means of the milled head 86 into that extreme position, in which what was so far the emergence surface 87 faces the entrance surface 88 of the corresponding objective prism 84 of the rear telemeter. 'Thereupon the setting drum 92 ofthe front telemeter is rotated, until its pointer 93 indicates the value infinity, at which indication the refracting prisms 90 and 91, deviating from the usual disposition, occupy that position, in which their refractive eect `is equal to that of a plano-parallel glass plate. An image of a ray pencil system coming from an object lying in front of the objective 105 ofthe optical system isformed by the said objective inthe separating prism system 81 of the front telemeter and is there split up into two part pencil systems, each of which is transmitted to one of the two corresponding objectives, 80, so that by each objective an lmage of the said object 1s presented to one of the objectives of the rear telemeter. Coincidence is now brought about with the aid of the setting drum 92 of the said rear telemeter for the said object, and the corresponding index- 93 is set so as totindicate the value infinity, whereupon the inner tube 75 and the objective prisms 85 ,of

Ithe front telemeter are moved into their v other extreme positions, so that the telemeter assumes its operative position. 1f

finally the index 104 of the joint indicating device be set so as to indicate the value ininity on the corresponding scale 102, on

setting the telemeters for any desired object, a value is indicated on this indicating device, which approximately corresponds to was correctly'adjusted or not.l lin the case of'larger angles of rotation of the refracting prlsms 90 and 291, instead of ing the innaief/ve dex 93 of the rear telemeterl adaptable, a glass wedge may be disposed in front of one of theobjectives of this telemeter, which,fo1*l bringing about coincidence for the' said object, on the indicating device being set for the value infinity, is to be rotated in a plane, which is perpendicular to the optical axis. ln this case the index 104 of the joint indieating device need also not be adaptable.

ll claim:

1. In a telemeter system a plurality of telemeters, a setting device for measuring purposescontained in each telemeter and an indicating device common to the said telemeters and consisting of a scale and an index, at least one of which two parts be# ing movable, and means for coupling the said setting devices and the said indicating device and for causing a -relative movement of the two'parts of the said indicating de vice, which movement corresponds to a mean value of the values given by the single telemeters. 1 f

2. lin a telemeter system a plurality of i telemeters, a setting device for measuring purposes contained 1n each telemeter and an indlcatlng device common to the said telemeters and consisting of a scale and an i index, at least one of which two parts being movable, and mechanical means for coupling the said'y setting devices'and the said indicating device and for causing a relative movement of the two parts of the said indicating device, which movement corresponds to a mean value of the values given by the single telemeters.

3. In a telemeter system two telemeters,

a commoncarrier for the reception of the said two telemeters, a setting device for measuring purposes in each telemeter, each of which devices comprises a system of refracting prisms, an indicating device common to t e said telemeters and consisting of a scale and an index, one of whichjtwo parts being movable, and diderential gearing, each of the said setting devices' being connected with one of the crown wheels of the said gearing and the movable part of the saidvindicating device being connected with the planet wheel of. the said gearing.

d. lin a telemeter system two adjacent self contained base telemeters with base lines of approximately the same length, the objective prisms of each telemeter being located in front of the objectives, a setting device for measuring purposes contained in each telemeter, an indicating device common to the two telemeters and consisting of ascale and said indicating device, which movement corresponds to a mean value of the values given by the single telemeters.

5. In a telemeter system two self contained base telemeters with parallel base lines of approximately the same length, a separating prism system in each telemeter, a common carrier for the reception of the two telemeters, the objective prisms of each telemeter being located in front of the objectives, a setting device formeasuring purposes contained in each telemeter, anv indicating device common to the two telemetrs and consisting of a' scale andan index, at least one of which two parts being movable, means for rotating the objective prisms of one of the telemeters in the` sighting plane through 90 to face with what were so far theirvemergence surfaces the entrance surfaces of the objective prisms of the other 20 axis, which is parallel tothe base lines, and means for coupling the said setting devices 25 and the said indicating deviceand for causing a relative movement' of the two parts of the said indicating device,fwhich movement corresponds to a mean value of the'values given by the single telemeters.

oTTo EDPENsTEiN. Witnesses: V

PAUL KRGER, RICHARD HAKU. 

